Call to a member function get() on null

<?php

namespace appmodels;

use dektriumusermodelsUser as BaseUser;

class User extends BaseUser
{
public function getBalance()
{
    return $this->hasOne(UserBalance::className(), ['user_id' => 'id']);
}

<?php
namespace appmodels;

use dektriumusermodelsRegistrationForm as BaseRegistrationForm;

class RegistrationForm extends BaseRegistrationForm
{
    public function signup()
    {
        Yii::$app->db->transaction(function() {
            (new UserBalance([
                'user_id' => $this->id,
                'silver_in' => 100
            ]))->save();
            // increase setting
            $value = SettingHelper::get('user.count') + rand(1, 10);
            SettingHelper::set('user.count', $value);
        });
    }
}

'modules' => [
    'rbac' => 'dektriumrbacRbacWebModule',
    'user' => [
        'class' => dektriumuserModule::className(),
        // 'identityClass' => 'dektriumusermodelsUser',
        // 'identityClass' => 'dektriumusermodelsRegistrationForm',
        'mailer' => [
            //'sender'                => 'no-reply@myhost.com', // or ['no-reply@myhost.com' => 'Sender name']
            'sender'                => 'swallowsveta97@yandex.ru',
            'welcomeSubject'        => 'Welcome subject',
            'confirmationSubject'   => 'Confirmation subject',
            'reconfirmationSubject' => 'Email change subject',
            'recoverySubject'       => 'Recovery subject',
        ],
        'controllerMap' => [
            'registration' => [
                'class' => dektriumusercontrollersRegistrationController::className(),
                'on ' . dektriumusercontrollersRegistrationController::EVENT_AFTER_REGISTER => function ($e) {
                    Yii::$app->response->redirect(array('/user/security/login'))->send();
                    Yii::$app->end();
                }
            ],
        ],
        'modelMap' => [
            'User' => 'appmodelsUser',
            'RegistrationForm' => 'appmodelsRegistrationForm',
        ],
        'enableUnconfirmedLogin' => true,
        'enableFlashMessages' => true,
        'enableRegistration' => true,
        'enableGeneratingPassword' => true,
        'enableUnconfirmedLogin' => false,
        'enablePasswordRecovery' => true,
        'enableAccountDelete' => false,
        'emailChangeStrategy' => 'dektriumuserModule::STRATEGY_DEFAULT',
        'recoverWithin' => 21600,
        'confirmWithin' => 21600,
        'cost' => 12,
        'admins' => ['admin']
    ],
],

<?php
namespace appmodels;

use apphelpersBalanceHelper;
use yiibaseInvalidParamException;
use yiidbActiveRecord;

class UserBalance extends ActiveRecord
{
    const CURRENCY_SILVER_IN = 'silver_in';
    const CURRENCY_SILVER_OUT = 'silver_out';
    const CURRENCY_GOLD_IN = 'gold_in';
    const CURRENCY_GOLD_OUT = 'gold_out';
    const CURRENCY_FACTORY_ONE = 'factory_one';
    const CURRENCY_FACTORY_TWO = 'factory_two';

    public static function tableName()
    {
        return '{{%user_balance}}';
    }

    public function rules()
    {
        return [
            ['user_id', 'integer'],
        ];
    }

    public function attributeLabels()
    {
        return [
            'silver_in' => Yii::t('app', 'Серебро'),
            'silver_out' => Yii::t('app', 'Серебро на вывод'),
            'gold_in' => Yii::t('app', 'Золото'),
            'gold_out' => Yii::t('app', 'Золото на вывод'),
            'factory_one' => Yii::t('app', 'Фабрика 1'),
            'factory_two' => Yii::t('app', 'Фабрика 2'),
        ];
    }

    public function getUser()
    {
        return $this->hasOne(User::className(), ['id' => 'user_id']);
    }

    public function get($currency)
    {
         $currentSum = Yii::$app->db->createCommand('
            SELECT `'.$currency.'`
            FROM {{%user_balance}}
            WHERE `user_id` = :user_id', [
            ':user_id' => $this->user_id
         ])->queryScalar();
         return BalanceHelper::toDigits($currency, $currentSum);
    }

    public function has($currency, $sum)
    {
        $currentSum = Yii::$app->db->createCommand('
            SELECT `'.$currency.'`
            FROM {{%user_balance}}
            WHERE `user_id` = :user_id', [
            ':user_id' => $this->user_id
        ])->queryScalar();

        return $currentSum >= BalanceHelper::toCoins($currency, $sum);
    }

    public function decrease($currency, $sum)
    {
        if ($this->has($currency, $sum)) {
            $sum = BalanceHelper::toCoins($currency, $sum);

            $rows = Yii::$app->db->createCommand('
                UPDATE {{%user_balance}}
                SET `' . $currency . '` = `' . $currency . '` - :sum
                WHERE `' . $currency . '` >= :sum
                AND `user_id` = :user_id', [
                ':sum' => $sum,
                ':user_id' => $this->user_id
            ])->execute();

            return $rows > 0;
        }
        return false;
    }

    public function increase($currency, $sum)
    {
        $sum = BalanceHelper::toCoins($currency, $sum);

        $rows = Yii::$app->db->createCommand('
            UPDATE {{%user_balance}}
            SET `' . $currency . '` = `' . $currency . '` + :sum
            WHERE `user_id` = :user_id', [
        ':sum' => $sum,
        ':user_id' => $this->user_id
        ])->execute();

        return $rows > 0;
    }

    public static function getCurrencyArray()
    {
        return [
            self::CURRENCY_SILVER_IN => Yii::t('app', 'Серебро'),
            self::CURRENCY_SILVER_OUT => Yii::t('app', 'Серебро на вывод'),
            self::CURRENCY_GOLD_IN => Yii::t('app', 'Золото'),
            self::CURRENCY_GOLD_OUT => Yii::t('app', 'Золото на вывод'),
            self::CURRENCY_FACTORY_ONE => Yii::t('app', 'Фабрика 1'),
            self::CURRENCY_FACTORY_TWO => Yii::t('app', 'Фабрика 2'),
        ];
    }

    public function getCurrencyString()
    {
        $currencies = self::getCurrencyArray();
        return isset($currencies[$this->currency]) ? $currencies[$this->currency] : '';
    }

}

<?php if (Yii::$app->user->isGuest) { ?>
    <?php } else { ?>
    <div class="main-p">
        <p><a href="#"><i class="fa fa-home" aria-hidden="true"></i>Серебро</a>
        <?= Yii::$app->user->identity->balance->get(UserBalance::CURRENCY_SILVER_IN) ?>
        <p><a href="#"><i class="fa fa-home" aria-hidden="true"></i>Серебро на вывод</a></li>
        <?= Yii::$app->user->identity->balance->get(UserBalance::CURRENCY_SILVER_OUT) ?>
        <p><a href="#"><i class="fa fa-home" aria-hidden="true"></i>Золото</a></li>
        <?= Yii::$app->user->identity->balance->get(UserBalance::CURRENCY_GOLD_IN) ?>
        <p><a href="#"><i class="fa fa-home" aria-hidden="true"></i>Золото на вывод</a></li>
        <?= Yii::$app->user->identity->balance->get(UserBalance::CURRENCY_GOLD_OUT) ?>
        <p><a href="#"><i class="fa fa-home" aria-hidden="true"></i>Фабрика 1</a></li>
        <?= Yii::$app->user->identity->balance->get(UserBalance::CURRENCY_FACTORY_ONE) ?>
        <p><a href="#"><i class="fa fa-home" aria-hidden="true"></i>Фабрика 2</a></li>
        <?= Yii::$app->user->identity->balance->get(UserBalance::CURRENCY_FACTORY_TWO) ?>
    </div>
    <?php } ?>